Laundry detergent compositions that comprise chelating agents are known. For example, the chelating agent tiron, 1,2-dihydroxybenzene-3,5-disulfonic acid, is known in the art of detergent compositions as a cleaning agent. Tiron delivers hydrophilic cleaning benefits, particularly on bleachable stains, and may also drive particulate cleaning via clay peptization, suspension, and/or synergy with polymeric dispersing systems. However, tiron and other related chelants are known to bind to ions of certain transition metals, which may be present as contaminants in detergent compositions, and form colored metal/chelant complexes. For example, tiron binds to ferric iron to form a burgundy red metal/tiron complex that can be detected at metal ion concentrations of 0.1 parts per million (ppm) or even lower. Many detergent compositions contain concentrations of soluble iron, such as ferric iron, as an impurity, and the concentration of ferric iron in these detergents is enough to form sufficient metal/chelant complexes to give the detergent a reddish color. Consumers may disfavor reddish-colored detergents, as a reddish color may be associated with, for example, rust. Furthermore, such color formation may make it difficult to create a consistently-colored finished product.
Laundry detergent compositions comprising bleach and a chelating agent are also known. It is believed that the chelant may bind to metal ions present in the composition or on the target fabric, resulting in, for example, a reduced rate of peroxygen bleach decomposition. Examples of such chelants include: phosphonate chelants, such as ethydronic acid and hydroxy-ethane diphosphonic acid (HEDP); polyfunctionally-substituted aromatic chelants, such as 1,2-dihydroxy-3,5-disulfobenzene (tiron); succinate chelants, such as ethylenediamine N,N′-disuccinic acid (EDDS); amino carboxylate chelants, such as diethylene triamine pentoacetate (DTPA) and propylene diamine tetracetic acid (PDTA); polycarboxylic acids of pyridine, such as dipicolinic acid; and others, including malonic acid and hydroxy-pyridine-N-oxides, e.g., 2-hydroxy-pyridine-1-oxide.
It would be desirable to produce a detergent composition—which is substantially free of bleach—that comprises a chelating agent and provides hydrophilic cleaning benefits, particularly on bleachable stains, without undesirable color formation. It has been discovered that such a detergent composition may be produced by specifically selecting and including certain derivatives of pyridine-N-oxide as the chelating agent in the detergent composition.